Oil plug

[Koppyscott]

This may be a real long shot, but does anyone know what size the plug is on the side of a 335 industrial (similar to a 3600) for checking rear end oil level? Someone prior to me has some random machine screw wrapped in teflon tape pressed into it. I’m planning to change the rear end hydraulic oil this weekend and I’d like to get the right plug back in. I’m referring to to small oil level check plug on the right side just above the foot board. I’ve tried every random bolt, 1/4” pipe plug, 1/8” pipe plug. Nothing fits.

 

[Jim.ME]

I think it was 1/4 NPT; someone will be along to confirm or correct that. There is a good chance the threads are messed up now and that is why the plugs you tried won't fit. You may need to try using a tap (coated with grease to hold chips) to clean the threads up.

 

[Hacke]

I know very little about this model, out of curiosity I looked at diagrams and as far as I understand, the slotted screw (#69, 5/16" - 24 UNF) goes into a nut and holds the return tube. In this diagram, there is no level plug:

https://www.mycnhstore.com/us/en/newhollandag/na/light-equipment/utility/nabs87uti002utility/3-cyl-utility-tractor/hydraulic-systems/flow-control-valve-assemblies/cn/925AB1CD-B8BF-E111-9FCE-005056875BD6/A4F5724F-E6BE-E111-9FCE-005056875BD6

In this diagram, there is a level plug (#4, square head 1/4" - 18 NPT):

Center Housing & Related Parts - 2600, 3600, 231, 531, 233, 333, 335 | New Holland Agriculture | MyCNH US Store

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A user manual shows only this:

 

[Hacke]

Just thinking, this image shows level plugs for other contemporary models. Perhaps you have a level plug in that area?

 

[Koppyscott]

In your second image, that would be the side of the transmission. Yes, there’s a plug there for that fluid level.

 

[Sean in PA]

My parts book says 1/4"-18 NPT as well. If a 1/4"-18 NPT doesn't fit then chances are that the threads were stripped out by a previous owner. Tap it to the next size or use an expanding plug.

 

[Hacke]

In your second image, that would be the side of the transmission. Yes, there’s a plug there for that fluid level.

Transmission and rear axle oil compartments are not connected, and should have a level plug each. I have this old image showing a 4000. Different details, but the same rear axle/transmission setup.

 

[Koppyscott]

Yes that’s correct, they’re separate. A foot apart or more. I’ll check a 1/4” plug again and let you guys know but I remember it being considerably bigger than the hole.

 

[Old Ford Mechanic]

Hacke has given you the correct info with figure 72. The smaller screw is there to hold a return tube inside the housing. It is supposed to have a seal that is probably missing thus, the reason for the teflon tape.

 

[Hacke]

Yes that’s correct, they’re separate. A foot apart or more. I’ll check a 1/4” plug again and let you guys know but I remember it being considerably bigger than the hole.

Are we talking about the shiny slotted screw in your image, or is it about another one hiding in the dark area?

 

[Koppyscott]

Yes, I can grab that screw and pull it straight out. As you can see by the grime, it leaks.

 

[Hacke]

Yes, I can grab that screw and pull it straight out. As you can see by the grime, it leaks.

According to the parts diagram, that would be an unthreaded through hole for a 5/16" screw. You say the hole is smaller than 1/4". Strange.

*** Edit
Sorry, my bad.
A 1/4" NPT plug has a major diameter of ~13.6 mm.
A 5/16" UNF screw has a major diameter of ~7.9 mm.

You are absolutely right about a 1/4" NPT plug is considerably larger than a through hole for a 5/16" screw.
***

 

[Hacke]

Most likely, a previous owner thought that the screw was a level plug. After discovering that the hole is unthreaded, there was a try to fix the issue with the help of teflon tape. Now you may have the return tube disconnected, at least it is not fixed.

 

[Koppyscott]

You’re right. Now that I’m back home I pulled the screw out. It’s an unthreaded .325 hole.

 

[Old Ford Mechanic]

You will need to find a seal for the screw. The top cover will need to be removed to realign the tube for attachment. Gasket or seal should be part # 81800802 from New Holland.

 

[Hacke]

I recall someone (I think it was Ultradog) from a forum wrote about a solution for a 3000. By working from the cover opening on the left side, a helper could manage to put the tube/nut in place while you rethreaded the screw on the other side. This model has some more parts inside, so it may not be possible.

If there is a transmission handbrake, I think it is impossible, there will be a gear in the way.

Anyhow, if there is a cover on the left side, you could, after draining the rear axle, take a peek inside.

 

[Koppyscott]

Oh geez, this turned into way more than trying to replace a plug. So if I’m understanding correctly that screw does belong there, it’s just supposed to be threaded into a tube and not the oil level plug I thought it was.

 

[Jim.ME]

Oh geez, this turned into way more than trying to replace a plug. So if I’m understanding correctly that screw does belong there, it’s just supposed to be threaded into a tube and not the oil level plug I thought it was.

That screw is not the plug you posted you were having issues getting to fit.

 

[Hacke]

Oh geez, this turned into way more than trying to replace a plug. So if I’m understanding correctly that screw does belong there, it’s just supposed to be threaded into a tube and not the oil level plug I thought it was.

No, it is not a level plug.
Click the first link in post #3. This will show a diagram, the screw is #69 and it goes into the nut #58.

*** Edit
Make sure you that you have the correct screw:
5/16'' - 24 x 1 1/4''
***

 

[Koppyscott]

I’ll double check it, thank you. Bigger concern now is that I potentially have a nut floating around inside somewhere. The image you sent earlier figure 72 looks very similar but what they have labeled as oil level plug, on my machine seems to be where the return line is coming from the oil cooler up front.